Magnetic core for saturable reactor, magnetic amplifier type multi-output switching regulator and computer having magnetic amplifier type multi-output switching regulator

ABSTRACT

A magnetic core for use in a saturable reactor made of an Fe-based soft-magnetic alloy comprising as essential alloying elements Fe, Cu and M, wherein M is at least one element selected from the group consisting of Nb, W, Ta, Zr, Hf, Ti and Mo, and having an alloy structure at least 50% in area ratio of which being fine crystalline particles having an average particle size of 100 nm or less. The magnetic core has control magnetizing properties of a residual operating magnetic flux density ΔBb of 0.12 T or less, a total control operating magnetic flux density ΔBr of 2.0 T or more, and a total control gain Gr of 0.10-0.20 T/(A/m) calculated by the equation: Gr=0.8×(ΔBr−ΔBb)/Hr, wherein Hr is a total control magnetizing force defined as a control magnetizing force corresponding to 0.8×(ΔBr−ΔBb)+ΔBb.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a magnetic core for use in asaturable reactor, a multi-output switching regulator controlling theoutput voltage by a magnetic amplifier, and a computer equipped withsuch a multi-output switching regulator.

[0002] The multi-output switching regulator has been used in personalcomputers and office computers. For example, in a PC AT-X type computer,a most typical desktop personal computer, a multi-output switchingregulator with five outputs, i.e., +5V output (1.5-20 A), +3.3V output(0-20 A), +12V output (0.2-8 A), −5V output (0-0.3 A) and −12V output(0-0.4 A) is used when a larger output capacity is required. In theabove five-output switching regulator, the main circuit comprises aforward converter with single switching element or a half bridgeconverter. The main output (+5V output) is controlled by a pulse-widthmodulation of a switching element located in a primary side of a maintransformer, and the secondary outputs (+3.3V, +12V, −5V and −12Voutputs) are controlled at the secondary side of the main transformer.

[0003] One of the methods for controlling the secondary outputs at thesecondary side of the main transformer is a control by a magneticamplifier located at the secondary side of the main transformer. Themagnetic amplifier basically comprises, as the main components, asaturable reactor, a diode and an error amplifier. This method hasadvantages of simultaneously attaining a small size, a high efficiency,a low noise generation and a high reliability, which have not beenattained by a control using a chopper circuit and a dropper circuitutilizing semiconductor elements. It has been known in the art that thecontrol by the magnetic amplifier is advantageous for controlling theoutput with a low voltage and a large load current, particularly in viewof a high efficiency, because the loss in the saturable reactor serve asa control element is small as compared with the loss in thesemiconductor control element used in the chopper circuit or the droppercircuit even when the load current is large. Therefore, in themulti-output switching regulator for the PC AT-X type personal computer,the magnetic amplifier has been widely used for controlling the +3.3 Vand +12 V outputs having a large load current. In the present invention,the switching regulator utilizing the magnetic amplifier is referred toas a magnetic amplifier type switching regulator.

[0004] The switching frequency of the magnetic amplifier typemulti-output switching regulator is usually set to about 50-200 kHz.Therefore, a Co-based amorphous core has been widely used as themagnetic core for the saturable reactor of the magnetic amplifier.However, in the magnetic amplifier type multi-output switching regulatorincorporated with a saturable reactor having the Co-based amorphouscore, the secondary output voltage being controlled by the magneticamplifier is lower than the reference value due to the voltage drop bythe saturable reactor when the load current increases even if the resetcurrent Ir for the saturable reactor is made zero. The output voltagedrop is attributable to a residual operating magnetic flux density ΔBbof the core and an unfavorable reset of the saturable reactor by areverse recovery current Irr from a diode connected in series to thesaturable reactor.

[0005] The voltage drop by the saturable reactor increases withincreasing residual operating magnetic flux density ΔBb when the coresize and the number of turns of the saturable reactor are constant.Also, the magnetic flux density ΔBr to be reset by the reverse recoverycurrent Irr from the diode is larger in a core which acquires a largercontrol magnetic flux density ΔB by a small control magnetizing forcewhen the core size and the number of turns of the saturable reactor areconstant.

[0006] In this connection, it has been known in the art that the voltagedrop by the saturable reactor is smaller in using an anisotropic 50%-Nipermalloy core than in using the Co-based amorphous core when the coresize and the number of turns of the saturable reactor are the same,because the anisotropic 50%-Ni permalloy core shows a small residualoperating magnetic flux density ΔBb and acquires a smaller controlmagnetic flux density ΔB when magnetized by the same control magneticforce as applied to the Co-based amorphous core. However, since theanisotropic 50%-Ni permalloy core shows a large core loss at a higherfrequency range, the switching frequency is limited to about 20 kHz atmost, and it has been recognized in the art that the use of theanisotropic 50%-Ni permalloy core at a switching frequency higher than20 kHz has been impractical, because such a use requires an extremelyincreased number of turns and causes a significant temperature rise ofthe saturable reactor. Therefore, the anisotropic 50%-Ni permalloy corefails to reduce the size of the magnetic amplifier type multi-outputswitching regulator and is not suitable for the application such as apersonal computer which requires a reduced size.

[0007] In the present invention, ΔB, ΔBb and ΔBr are defined as shown inFIG. 5, wherein Br is a residual magnetic flux density, H is a controlmagnetizing force, and H_(Lm) is the maximum value of a gate magnetizingforce.

[0008] In the magnetic amplifier type multi-output switching regulator,for example, used in the PC AT-X type desktop personal computer, boththe main output (+5V output) and the secondary output (+3.3V output) areusually taken out of the same secondary winding of the transformer,because the potential difference between the +5V output and the +3.3Voutput is small. Therefore, it has been known that the voltage drop inthe +3.3V output cannot be avoided by using a secondary winding for the+5V output and another secondary winding for the +3.3V output with anumber of turns larger than that of the secondary winding for the +5Voutput.

[0009] To eliminate the above disadvantage, Japanese Patent PublicationNo. 2-61177 discloses a magnetic amplifier in which a reset circuitcomprising series-connected rectifying diode and control element isconnected in parallel to both the ends of a saturable reactor, therebyto control the reset of the saturable reactor by the control element.However, the proposed magnetic amplifier requires at least fouradditional circuit elements to spoil the advantage such as a smallnumber of circuit elements of the magnetic amplifier type multi-outputswitching regulator.

[0010] Japanese Patent Laid-Open No. 63-56168 discloses a magneticcontrol type switching regulator in which a saturable reactor has awinding for forming a short circuit in addition to a main winding foroutput, thereby to avoid the drop in the output voltage attributable toa dead time and an unfavorable reset of the saturable reactor by thereverse recovery current Irr of a rectifying diode. However, theproposed method is insufficient in preventing the voltage drop of thesaturable reactor as compared with the method disclosed in JapanesePatent Publication No. 2-61177, because the additional winding for theshort circuit, an additional diode serving as an active element in theshort circuit and the reverse recovery current from the additional diodecause the voltage drop of the saturable reactor.

[0011] Japanese Patent Publication No. 7-77167 discloses a magnetic coremade of an Fe-based alloy containing Fe, Cu and M as essentialcomponents, wherein M is at least one element selected from the groupconsisting of Nb, W, Ta, Zr, Hf, Ti and Mo. It is described that thesaturable reactor made of the proposed magnetic core has a highsquareness ratio and shows a small core loss and a high magnetic fluxdensity. However, the proposed magnetic core shows an increased ΔBb dueto the impact or shock thereon during the production process, and thisproblem has not been avoided by the production method disclosed therein.Therefore, a magnetic amplifier type multi-output switching regulatorutilizing a saturable reactor made of the proposed magnetic coregenerates an output voltage lower than the reference value when the loadcurrent is large.

OBJECT AND SUMMARY OF THE INVENTION

[0012] Accordingly, an object of the present invention is to provide ahighly reliable multi-output switching regulator having a magneticamplifier constructed by a reduced number of circuit elements and beingcapable of providing a stable output.

[0013] As a result of the intense research in view of the above objects,the inventors have found that a saturable reactor having a magnetic coremade of an Fe-based alloy having a specific chemical composition, aspecific alloy structure and specific control magnetizing propertiesexhibits a low voltage drop when a reset current Ir is zero and acquiresa large control magnetic flux density ΔB by a small reset current Ir.With such a saturable reactor, the number of turns of the winding on thesaturable reactor has been reduced and the temperature rise of thesaturable reactor at a large load current and at no load has beenminimized. Based on these findings, the inventors have further foundthat a multi-output switching regulator utilizing a magnetic amplifierhaving such a saturable reactor prevents the secondary output voltagebeing controlled by the magnetic amplifier from becoming lower than thereference value even when the load current increases, and can beoperated at a higher frequency, thereby to provide a magnetic amplifiertype multi-output switching regulator with a reduced size, a highefficiency and a high reliability.

[0014] Thus, in a first aspect of the present invention, there isprovided a magnetic core for use in a saturable reactor made of anFe-based soft-magnetic alloy comprising as essential alloying elementsFe, Cu and M, wherein M is at least one element selected from the groupconsisting of Nb, W, Ta, Zr, Hf, Ti and Mo, and having an alloystructure at least 50% in area ratio of which being fine crystallineparticles having an average particle size of 100 nm or less, wherein themagnetic core has, when measured at a core temperature of 25° C. using a50 kHz monopolar rectangular voltage with an on-duty ratio of 0.5,control magnetizing properties of: (1) 0.12 T or less of a residualoperating magnetic flux density ΔBb; (2) 2.0 T or more of a totalcontrol operating magnetic flux density ΔBr; and (3) 0.10-0.20 T/(A/m)of a total control gain Gr calculated by the equation: Gr=0.8×(ΔBr−ΔBb)/Hr, wherein Hr is a total control magnetizing force definedas a control magnetizing force corresponding to 0.8×(ΔBr−ΔBb)+ΔBb.

[0015] In a second aspect of the present invention, there is provided amulti-output switching regulator having a magnetic amplifier comprisinga saturable reactor which is constructed from the magnetic core asdefined above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a schematic diagram showing a circuit of the magneticamplifier type multi-output switching regulator of the presentinvention;

[0017]FIG. 2 is a schematic view showing a magnetic core of the presentinvention;

[0018]FIG. 3 is a schematic view showing a saturable reactor of thepresent invention;

[0019]FIG. 4 is a schematic diagram showing a measuring circuit used formeasuring the control magnetizing properties; and

[0020]FIG. 5 is an operating hysteresis loop showing the definitions ofthe control magnetizing properties.

DETAILED DESCRIPTION OF THE INVENTION

[0021] The magnetic core of the present invention is produced from anFe-based soft magnetic alloy comprising as essential alloying elementsFe, Cu and M, wherein M is at least one element selected from the groupconsisting of Nb, W, Ta, Zr, Hf, Ti and Mo, at least 50% in area ratioof the alloy structure being fine crystalline particles having anaverage particle size of 100 nm or less.

[0022] The Fe-based soft magnetic alloy used for the magnetic coreaccording to the present invention has the chemical compositionrepresented by the general formula:

(Fe_(1-a)X_(a))_(100-x-y-z-α)Cu_(x)Si_(y)B_(z)M_(α)M′_(β)M″_(γ)

[0023] wherein X is Co and/or Ni, M is at least one element selectedfrom the group consisting of Nb, W, Ta, Zr, Hf, Ti and Mo, M′ is atleast one element selected from the group consisting of V, Cr, Mn, At,platinum group elements, Sc, Y, rare earth elements, Au, Zn, Sn and Re,M″ is at least one element selected from the group consisting of C, Ge,P, Ga, Sb, In, Be and As, and a, x, y, z, α, β and γ respectivelysatisfy 0≦a≦0.5, 0.1≦x≦3, 0≦y≦30, 0≦z≦25, 5≦y+z≦30, 0.1≦α≦30, 0≦β≦10 and0≦γ≦10.

[0024] Fe may be substituted by Co and/or Ni in the range of up to a=0.5. When “a” exceeds 0.5, the control magnetizing properties of themagnetic core are deteriorated. However, to have good magneticproperties such as low core loss and magnetostriction, “a” is preferably0-0.1. Particularly; to provide a low magnetostriction alloy, the rangeof “a” is preferably 0-0.05.

[0025] Cu is an indispensable element, and its content “x” is 0.1-3atomic %. When it is less than 0.1 atomic %, substantially no effect ofadding Cu can be obtained. On the other hand, when it exceeds 3 atomic%, the resulting magnetic core has poor control magnetizing propertiesas compared with those containing no Cu.

[0026] Cu and Fe have a positive interaction parameter so that theirsolubility is low. Accordingly, when the alloy is heated while it isamorphous, iron atoms or copper atoms tend to gather to form clusters,thereby producing compositional fluctuation. This produces a lot ofdomains likely to be crystallized to provide nuclei for generating finecrystalline particles. These crystalline particles are based on Fe, andsince Cu is substantially not soluble in Fe, Cu is ejected from the finecrystalline particles, whereby the Cu content in the vicinity of thecrystalline particles becomes high. This presumably suppresses thegrowth of crystalline particles. Because of the formation of a largenumber of nuclei and the suppression of the growth of crystallineparticles by the addition of Cu, the crystalline particles are madefine, and this phenomenon is accelerated by the addition of at least oneessential base metal element M selected from the group consisting of Nb,W, Ta, Zr, Hf, Ti and Mo.

[0027] The essential base metal elements M have a function of elevatingthe crystallization temperature of the alloy. Synergistically with Cuhaving a function of forming clusters and thus lowering thecrystallization temperature, M suppresses the growth of the precipitatedcrystalline particles, thereby making them fine. The content of M (“α”)is 0.1-30 atomic %. Without adding the essential base metal element, thecrystalline particles are not fully made fine and thus the soft magneticproperties of the resulting magnetic core are poor. A content exceeding30 atomic % causes an extreme decrease in saturation magnetic fluxdensity. Particularly Nb and Mo are effective, and particularly Nb actsto keep the crystalline particles fine, thereby providing excellent softmagnetic properties.

[0028] Si and B are elements particularly for making the alloy structurefine. The Fe-based soft magnetic alloy is usually produced by onceforming an amorphous alloy with the addition of Si and B, and thenforming fine crystalline particles by heat treatment. The content of Si(“y”) and that of B (“z”) are 0≦y≦30 atomic %, 0≦z≦25 atomic %, and5≦y+z≦30 atomic %, because the magnetic core would have an extremelyreduced saturation magnetic flux density if otherwise.

[0029] M′, which is at least one element selected from the groupconsisting of V, Cr, Mn, At, platinum group elements, Sc, Y, rare earthelements, Au, Zn, Sn and Re, may be optionally added for the purpose ofimproving corrosion resistance or magnetic properties and of adjustingmagnetostriction, but its content is at most 10 atomic %. When thecontent of M′ exceeds 10 atomic %, an extreme decrease in a saturationmagnetic flux density occurs.

[0030] The Fe-based soft magnetic alloy may contain 10 atomic % or lessof at least one element M″ selected from the group consisting of C, Ge,P, Ga, Sb, In, Be and As. These elements are effective for making thealloy amorphous, and when added with Si and B, they help make the alloyamorphous and also are effective for adjusting the magnetostriction andCurie temperature of the alloy.

[0031] The Fe-based soft magnetic alloy used in the present inventionhas an alloy structure, at least 50% in area ratio of which consists offine crystalline particles when determined by a photomicrograph. Thesecrystalline particles are based on α-Fe having a bcc structure, in whichSi and B, etc. are dissolved. These crystalline particles have anextremely small average particle size of 100 nm or less, and areuniformly distributed in the alloy structure. Incidentally, the averageparticle size of the crystalline particles is determined bymicrographically measuring the maximum size of each particle andaveraging them. When the average particle size exceeds 100 nm, good softmagnetic properties are not obtained. The lower limit of the averageparticle size is usually about 5 nm. The remaining portion of the alloystructure other than the fine crystalline particles may be mainlyamorphous. Even with fine crystalline particles occupying substantially100% of the alloy structure, the Fe-based soft magnetic alloy hassufficiently good magnetic properties.

[0032] The Fe-based soft magnetic alloy and the magnetic core of thepresent invention are produced, for example, by the following method.First, an alloy melt having the above chemical composition is rapidlyquenched by known liquid quenching methods such as a single roll method,a twin roll method, etc. to form amorphous alloy ribbons. Usuallyamorphous alloy ribbons have a thickness of 5-100 μm or so, and thosehaving a thickness of 25 μm or less are particularly suitable asmagnetic core materials for high-frequency use. The amorphous alloys maycontain crystal phases, but the alloy structure is preferred to besubstantially amorphous to make sure the formation of uniform finecrystalline particles by a subsequent heat treatment.

[0033] The amorphous ribbon is then wound to a toroidal shape whileapplying a tension in the length direction of the amorphous ribbon. Thetension is 20 gf or less per mm width of the ribbon, and preferably 12gf or less per mm width. By applying the tension within the above range,the stress generated in the amorphous ribbon is reduced to prevent theresidual operating magnetic flux density ΔBb of the magnetic core fromincreasing. The thickness tolerance of the toroidally wound ribbonshould be within the range of “width of ribbon+0.3 mm” so as to preventthe increase in the residual operating magnetic flux density ΔBb due tothe impact or shock onto the toroidal magnetic core during theproduction of the saturable reactor. The application of the tension ofthe above range and the thickness tolerance within the above range areimportant for the magnetic core to acquire the control magnetizingproperties specified in the present invention. An insulating coatingmade of ceramics, etc. may be interposed between the adjacent ribbonlayers by laying the insulating coating on the ribbon and winding themtogether.

[0034] The toroidally wound ribbon is then subjected to heat treatmentwhile applying a magnetic field of 200 A/m or more along the magneticpath of the wound ribbon in an inert gas atmosphere such as nitrogenatmosphere. The temperature is raised from room temperature to atemperature at which the amorphous ribbon is not crystallized, usually440-480° C. although dependent on the chemical composition of the alloy,at a temperature rising rate of 5-15° C./min, and maintained there for10-60 minutes. By the above pre-heating, the temperature gradientproduced in the heat-treating furnace during the temperature rise isminimized. The temperature of the pre-heating is preferred to be ashigher as possible unless the crystallization is initiated. After thepre-heating, the temperature is raised to 540-580° C. at a temperaturerise rate of 1-5° C./min and maintained there for 0.5-2 hours tocrystallize the amorphous ribbon. Then, the temperature is lowered toabout 100° C. at a cooling rate of 1.5-7.3° C./min, and thereafterallowed to cool down to room temperature, thereby to obtain a toroidalmagnetic core of the present invention, as shown in FIG. 2, having asize of 6-100 mm in outer diameter, 4-80 mm in inner diameter and 2-25mm in thickness.

[0035] The magnetic core thus produced is placed in an insulating resincase made of polyethylene terephthalate, etc. with a silicone grease,and a winding having suitable number of turns is wound over itsperimeter to obtain a saturable reactor as shown in FIG. 3. In thepresent invention, a high performance is obtained in a reduced number ofturns.

[0036] The magnetic core produced in the manner as described above hasthe following control magnetizing properties when measured at a coretemperature of 25° C. while operated by 50 kHz monopolar rectangularvoltage with an on-duty ratio of 0.5.

[0037] The residual operating magnetic flux density ΔBb is 0.12 T orless, and preferably 0.08 T or less. ΔBb higher than 0.12 Tdetrimentally narrowers the controlable range of the output of themagnetic amplifier when driven at 20 kHz or higher frequency. The totalcontrol operating magnetic flux density ΔBr is 2.0 T or more, andpreferably 2.0-3.0 T. ΔBr less than 2.0 T is unfavorable because thesaturable reactor used in the magnetic amplifier requires an increasednumber of turns when driven at 20 kHz or higher frequency.

[0038] The total control gain Gr is 0.10-0.20 T/(A/m). The total controlgain Gr is calculated form the following equation:

Gr=0.8×(ΔBr−ΔBb)/Hr

[0039] wherein Hr is a total control magnetizing force defined as acontrol magnetizing force corresponding to 0.8×(ΔBr−ΔBb)+ΔBb. When Gr isoutside the above range, the saturable reactor in the magnetic amplifierrequires an extremely large control electric power.

[0040] The above control properties were measured using a measuringcircuit as shown in FIG. 4. A winding N_(L), corresponding to an outputwinding of a saturable reactor SR used in the magnetic amplifier, isconnected to an AC powder supply Eg through a resistor R_(L), A windingNc is a control winding, and connected to a variable DC power supply Ecthrough an inductor Lc and a resistor Rc. A winding Nv is a winding fordetermining ΔB. Q is a switching transistor. The integral value of theterminal voltage e_(v) over the period of dead time was determined by adigital oscilloscope Os, which was then divided by the number of turnsof the winding Nv and the effective cross-sectional area of the core toobtain ΔB. As shown in FIG. 5, ΔBb is a difference between the maximummagnetic flux density Bm and the residual magnetic flux density Br. ΔBris related to ΔB by the equation of ΔBr=ΔB−ΔBb. The control magnetizingforce H was obtained by dividing a product of a measured value of i_(c)and the number of turns of the winding Nc by an average magnetic path ofthe core.

[0041] In FIG. 1, shown is a circuit of a preferred embodiment of themagnetic amplifier type multi-output switching regulator having thesaturable reactor of the present invention. The switching regulatorcomprises a primary circuit at a primary side of a main transformer 4,and a secondary circuit at a secondary side of the main transformer 4.

[0042] The primary circuit basically comprises an input DC power source1, a switching element 2 (MOS-FET: metal oxide semiconductor-fieldeffect transistor) and a primary winding 5, each being interconnected inseries. A diode 3 and a second primary winding 6 are furtherincorporated into the primary circuit as shown in FIG. 1.

[0043] The secondary circuit comprises a main output circuit forcontrolling and stabilizing a main output V1 (between output terminals16 and 25 by a pulse-width controlling function of the switching element2, and a secondary output circuit. The main output circuit shown in FIG.1 is a forward converter with single switching element and basicallycomprises an input DC power source 1, the switching element 2, atransformer 4, diodes 21, 22, a smoothing choke coil 23, and a smoothingcapacitor 12. The secondary output circuit comprises a magneticamplifier for controlling and stabilizing a secondary output V2 (betweenoutput terminals 16 and 15), diodes 9, 10, 14, a smoothing choke coil11, and a smoothing capacitor 12. The magnetic amplifier shown in FIG. 1is a Ramey's quick-response type and comprises a saturable reactor 8, adiode 9, a diode 14 and an error amplifier 13. The anode portion of thediode 9 is connected to the saturable reactor 8, while the cathodeportion of the diode 14 is connected to a node between the saturablereactor 8 and the diode 9 in a shunt configuration, and the anodeportion thereof is connected to an output terminal 16 through the erroramplifier 13.

[0044] In a preferred embodiment of the magnetic amplifier typemulti-output switching regulator of the present invention, both the mainoutput circuit and the secondary output circuit are respectivelyconnected to the same end of a secondary winding 7. With such aconstruction, the voltage drop in the secondary output being controlledby the magnetic amplifier is effectively avoided without usingadditional elements or circuits as proposed in the prior art such asJapanese Patent Publication No. 2-61177 and Japanese Patent Laid-OpenNo. 63-56168 mentioned above even when the load current of the secondaryoutput increases, thereby to make it possible to obtain a small-sizemagnetic amplifier type multi-output switching regulator with a highefficiency and a high reliability.

[0045] A further reduction in size and a further improvement in theefficiency and reliability can be achieved when the output voltage ofthe main output circuit is +5V and the output voltage of the secondaryoutput circuit is +3.3V, because the secondary output voltage isprevented from being lower than the reference value of +3.135V even whenthe load current of the secondary output increases.

[0046] The switching frequency of the magnetic amplifier typemulti-output switching regulator is preferably 30-150 kHz in view ofobtaining a small-size saturable reactor with a high efficiency and ahigh reliability. In addition, since the above switching frequency rangeis lower than the frequency range regulated by CISPR (ComitéInternational Spécial des Perturbations Radioélectriques) Pub. 11, thenoise terminal voltage is easily avoided.

[0047] The present invention will be further described while referringto the following Examples which should be considered to illustratevarious preferred embodiments of the present invention.

EXAMPLE 1

[0048] Each melt having respective chemical composition shown in Table 1was formed into a ribbon of 5 mm in width and 20 μm in thickness. TheX-ray diffraction and the transmission electron photomicrograph of eachribbon showed that the resulting ribbon was substantially amorphous.

[0049] Next, the amorphous ribbon was formed into a toroidal woundribbon while applying a tension in the length direction of the ribbon.The tension and the thickness tolerance of the wound ribbon are shown inTable 1.

[0050] The toroidal wound ribbon was then subjected to heat treatment innitrogen atmosphere while applying a magnetic field of 200 A/m in thedirection of magnetic path of the wound ribbon. Specifically thetoroidal wound ribbon was heated from room temperature to 470° C. over 1hour and kept at 470° C. for 30 minutes. Then, the temperature wasraised from 470° C. to a temperature shown in Table 1 over 30 minutesand kept there for one hour to crystallize the amorphous ribbon. Thetoroidal wound ribbon thus treated was cooled from 540° C. to 100° C.over 3 hours, and allowed to cool down in air to room temperature,thereby obtaining each toroidal magnetic core. Further, other magneticcores were produced by winding amorphous ribbon (Comparative Examples15-17) or permalloy ribbon (Comparative Examples 18-19).

[0051] The size of the magnetic cores thus produced was 10 mm in innerdiameter, 13 mm in outer diameter and 5 mm in thickness. TABLE 1 CoreHeat Mag- Chemical Ten- Thick- Treatment netic Composition sion nessTemperature Field No. (atomic %) (gf) (mm) (° C.) (A/m) Inven- tion  1Fe₇₄Cu_(1.5)Si_(13.5)B₉Nb₂  60 5.2 540 200  2 Fe₇₄Cu_(1.5)Si_(13.5)B₉Nb₂100 5.3 540 200  3 Fe₇₄Cu_(1.5)Si_(13.5)B₉Mo₂  60 5.3 540 200  4Fe₇₄Cu_(1.5)Si_(13.5)B₉Mo₂ 100 5.2 540 200  5 Fe₇₂Cu₁Si₁₄B₈Zr₅  60 5.3540 200  6 Fe₇₁Cu₁Si₁₄B₉Nb₅  60 5.2 540 200 Com- parison  7Fe₇₄Cu_(1.5)Si_(13.5)B₉Nb₂ 100 5.3 590 200  8 Fe₇₄Cu_(1.5)Si_(13.5)B₉Nb₂100 5.4 540 200  9 Fe₇₄Cu_(1.5)Si_(13.5)B₉Nb₂ 120 5.3 540 200 10Fe₇₄Cu_(1.5)Si_(13.5)B₉Mo₂ 100 5.3 590 200 11 Fe₇₄Cu_(1.5)Si_(13.5)B₉Mo₂120 5.2 540 200 12 Fe₇₂Cu₁Si₁₄B₈Zr₅ 100 5.2 590 200 13 Fe₇₁Cu₁Si₁₄B₉Nb₅100 5.4 540 200 14 Fe₇₀Cu₁Si₁₄B₈Nb₇ 120 5.2 540 200 15 Fe₇₀Ni₈Si₁₃B₉ 1005.2 400 400 (Amorphous) 16 Co_(69.5)Fe_(0.5)Mn₆Si₁₅B₉ 100 5.3 400 400(Amorphous) 17 Co₆₇Fe₄Mo_(1.5)Si_(16.5)B₁₁ 100 5.2 400 400 (Amorphous)18 50 wt. % Ni-Fe — 5.1 — — permalloy 19 80 wt. % Ni-Fe — 5.2 — —permalloy

[0052] The control magnetizing properties (ΔBr, ΔBb, Hr and Gr) ofmagnetic core were measured using the measuring circuit shown FIG. 4.The results are shown in Table 2. TABLE 2 No. ΔBr (T) ΔBb (T) Hr (A/m)Gr (T/(A/m)) Invention  1 2.48 0.05 13.1 0.148  2 2.47 0.08 11.8 0.162 3 2.48 0.07 15.4 0.125  4 2.48 0.10 12.9 0.148  5 2.30 0.06 17.5 0.102 6 2.04 0.07 8.1 0.195 Comparison  7 2.49 0.03 21.4 0.092  8 2.48 0.099.4 0.203  9 2.48 0.14 10.0 0.187 10 2.48 0.04 20.5 0.095 11 2.47 0.1310.2 0.184 12 2.31 0.06 20.7 0.087 13 2.03 0.09 7.0 0.222 14 1.91 0.1010.7 0.135 15 2.80 0.12 44.4 0.048 16 1.51 0.03 13.8 0.086 17 1.06 0.055.9 0.137 18 2.97 0.03 84.6 0.028 19 1.41 0.14 27.6 0.037

[0053] As seen from Table 2, Nos. 9, 11, 14 failed to show the controlmagnetizing properties required in the present invention due to atension larger than 20 gf/mm width. Since the thickness tolerance waslarger than 0.3 mm, Nos. 8 and 13 also failed to meet the requirement ofthe present invention. In addition, the temperature for crystallizationwas 590° C., Nos. 7, 10 and 12 also failed to meet the requirement ofthe present invention.

[0054] A conductive wire was wound around each magnetic core afterplacing it in a resin case so as to have the number of turns shown inTable 4 to produce each saturable reactor as shown in FIG. 3. Eachmagnetic amplifier type two-output switching regulator as shown in FIG.1 was constructed by using the saturable reactor thus produced, and thecontrol performance, the temperature rise and the reset current at noload were measured. The switching regulator was operated at a switchingfrequency of 50 kHz under the following conditions. TABLE 3 Input MainOutput (V1) Secondary Output (V2) Voltage Output Voltage Load CurrentOutput Voltage Load Current (V) (V) (A) (V) (A) 90 to 187 +5.0 1 to 20+3.3 0 to 20

[0055] The temperature rise ΔT was measured on the surface of thesaturable reactor one hour after the operation was initiated whileair-cooling the saturable reactor with a cooling fun stopped. Thecontrol performance was judged as “good” when the output voltage of thesecondary output V2 was +3.135 V to +3.465 V, and “poor” if otherwise.TABLE 4 Temperature Rise ΔT (° C.) Reset Number of Control MaximumCurrent No. Turns Performance No Load Load (mA) Invention  1 8 good 2235 35  2 8 good 21 35 32  3 8 good 26 37 39  4 8 good 22 35 34  5 9 good25 38 42  6 10  good 17 37 27 Comparison  7 8 good 27 42 41  8 8 poor 1833 25  9 8 poor 18 32 23 10 8 good 36 48 57 11 8 poor 18 33 24 12 9 good31 44 50 13 10 poor 12 39 15 14 11 good 14 46 21 15 8 poor 61 72 93 1613 good 10 41 20 17 17 good  6 58  5 18 16 good 39 84 108  19 13 poor 2357  32

[0056] The surrounding temperature is usually controlled to about 50° C.or lower for a satisfactory operation of the switching regulator. Whenthe surrounding temperature is 50° C., the temperature rise of thesurrounding atmosphere from room temperature is about 20° C. Therefore,considering the insulating grade E (JIS C 4003) of the insulatingmaterial constituting the parts of the switching regulator, thetemperature rise ΔT of the surface of the saturable reactor should beregulated to 40° C. or lower. The insulating grade E of JIS C 4003 meansinsulation sufficiently withstanding a temperature of 120° C.

[0057] As seen from Table 4, any of the comparative saturable reactors(Nos. 7-19) showed a poor control performance and/or a high temperaturerise. Therefore, the size of the core used in the comparative saturablereactor should be increased to ensure a satisfactory operation of theswitching regulator, thereby resulting in an unfavorable increase in thesize of apparatus.

[0058] On the other hand, the switching regulators utilizing thesaturable reactors of the present invention showed a good controlperformance and a temperature rise ΔT lower than 40° C., whereas thenumber of turns was small and the size of the magnetic core was small,thereby enabling to reduce the size of the switching regulator.

[0059] Also, the results showed that the reset current at no load was 42mA, at most, in the present invention. This enhances the efficiency ofthe switching regulator because the control power consumed is low.

EXAMPLE 2

[0060] The control performance, the temperature rise and the resetcurrent at no load were measured in the same manner as above except forchanging the switching frequency to 100 kHz. TABLE 5 Temperature Rise ΔT(° C.) Reset Number of Control Maximum Current No. Turns Performance NoLoad Load (mA) Invention  1 7 good 24 34 45  2 7 good 23 33 43  3 7 good29 39 52  4 7 good 25 35 46  5 7 good 28 39 56  6 7 good 19 31 36Comparison  7 7 good 32 43 55  8 7 poor 20 31 34  9 7 poor 22 32 32 10 7good 39 51 77 11 7 poor 20 31 33 12 7 good 39 49 75 13 7 poor 16 28 2414 8 good 19 53 34 15 — — — — — 16 8 good 16 43 46 17 8 good 11 41 21 18— — — — — 19 9 poor 37 69 78

[0061] As seen from Table 5, any of the comparative saturable reactors(Nos. 7-19) showed a poor control performance and/or a high temperaturerise. In particular, the measurements were not practicable in Nos. 15and 18 due to extreme temperature rise. Therefore, the size of the coreused in the comparative saturable reactor should be increased to ensurea satisfactory operation of the switching regulator, thereby resultingin an unfavorable increase in the size of apparatus.

[0062] On the other hand, the switching regulators utilizing thesaturable reactors of the present invention showed a good controlperformance and a temperature rise ΔT lower than 40° C., whereas thenumber of turns was small and the size of the magnetic core was small,thereby enabling to reduce the size of the switching regulator. Also,the results showed that the reset current at no load was 56 mA, at most,in the present invention. This enhances the efficiency of the switchingregulator because the control power consumed is low.

EXAMPLE 3

[0063] The control performance, the temperature rise and the resetcurrent at no load were measured in the same manner as above except forchanging the switching frequency to 150 kHz. TABLE 6 Temperature Rise ΔT(° C.) Reset Number of Control Maximum Current No. Turns Performance NoLoad Load (mA) Invention  1 5 good 28 35 87  2 5 good 27 35 82  3 5 good32 39 94  4 5 good 28 36 88  5 5 good 31 39 97  6 5 good 22 32 69Comparison  7 5 good 38 46 108   8 5 poor 24 31 65  9 5 poor 27 35 61 106 good 39 56 121  11 5 poor 23 32 63 12 6 good 38 56 119  13 5 poor 1930 47 14 6 good 23 43 54 15 — — — — — 16 6 good 29 48 69 17 6 good 18 4137 18 — — — — — 19 9 poor 39 83 112 

[0064] As seen from Table 6, any of the comparative saturable reactors(Nos. 7-19) showed a poor control performance and/or a high temperaturerise. In particular, the measurements were not practicable in Nos. 15and 18 due to extreme temperature rise. Therefore, the size of the coreused in the comparative saturable reactor should be increased to ensurea satisfactory operation of the switching regulator, thereby resultingin an unfavorable increase in the size of apparatus.

[0065] On the other hand, the switching regulators utilizing thesaturable reactors of the present invention showed a good controlperformance and a temperature rise ΔT lower than 40° C., whereas thenumber of turns was small and the size of the magnetic core was small,thereby enabling to reduce the size of the switching regulator. Also,the results showed that the reset current at no load was 97 mA, at most,in the present invention. This enhances the efficiency of the switchingregulator because the control power consumed is low.

EXAMPLE 4

[0066] The dependency of the number of turns, the control performance,the maximum temperature rise ΔTmax and the reset current at no load onthe switching frequency was evaluated in the same manner as in Example 1while using the magnetic cores of Nos. 2, 5, 6, 8, 10, 14, and 16-18.TABLE 7 Number of Turns 100 150 200 No. 20 kHz 30 kHz 50 kHz kHz kHz kHzInvention  2 18 12 8 7 5 5  5 18 12 8 7 5 5  6 18 12 8 7 5 5 Comparison 8 18 12 8 7 5 5 10 18 12 8 7 6 5 14 22 15 11 8 6 5 16 32 21 13 8 6 5 1742 28 17 8 6 5 18 15 15 16 — — —

[0067] TABLE 8 Control Performance 100 150 200 No. 20 kHz 30 kHz 50 kHzkHz kHz kHz Invention  2 good good good good good good  5 good good goodgood good good  6 good good good good good good Comparison  8 poor poorpoor poor poor poor 10 good good good good good good 14 poor good goodgood good good 16 poor poor good good good good 17 poor poor good goodgood good 18 good good good — — —

[0068] TABLE 9 Maximum Temperature Rise ΔTmax ° C.) 100 150 200 No. 20kHz 30 kHz 50 kHz kHz kHz kHz Invention  2 47 38 35 33 35 40  5 49 40 3839 39 45  6 44 36 33 31 32 36 Comparison  8 45 36 33 31 31 35 10 59 5248 51 56 57 14 62 53 46 53 43 45 16 73 56 41 43 48 51 17 87 71 58 41 4142 18 39 55 84 — — —

[0069] TABLE 10 Reset Current at No Load (mA) 100 150 200 No. 20 kHz 30kHz 50 kHz kHz kHz kHz Invention  2 9 16 33 41 76 93  5 11 18 35 45 82102  6 7 12 25 33 61 76 Comparison  8 7 14 28 37 67 83 10 16 25 47 62113 144 14 8 17 32 41 74 89 16 5 8 16 46 66 109 17 3 4 6 21 28 43 18 5878 97 — — —

[0070] As seen from the results, the switching regulators of the presentinvention simultaneously satisfied the requirements of a good controlperformance and the maximum temperature rise ΔTmax of 40° C. or lower atthe switching frequency over a range of 30 kHz to 150 kHz. It wouldappear that such a simultaneous satisfaction cannot be attained by usingthe comparative magnetic cores.

[0071] Namely, when the switching frequency is set in the range of30-150 kHz, which is lower than the lower limit of the frequency rangeregulated by CISPR Pub. 11, the magnetic cores of the present inventionare advantageous over the comparative magnetic cores in producing asaturable reactor and a switching regulator with a reduced size, a highefficiency and a high reliability. Also, the noise terminal voltage canbe easily avoided by using the magnetic cores of the present invention.In addition, the number of turns can be reduced by using the magneticcore of the present invention without sacrificing the performance of theswitching regulator in a broad switching frequency of 30-150 kHz. Thisenhances the productivity.

[0072] As described above, the magnetic core of the present inventionprovides a saturable reactor having a low voltage drop without usingadditional circuit elements as required in the prior art even when theload current is large, and having a low temperature rise even whenoperated at a higher frequency. A magnetic amplifier type multi-outputswitching regulator constructed by the saturable reactor having themagnetic core of the present invention has various advantages such as agood control performance even when the load current is large, a lowtemperature rise, a small size, a high efficiency, a reduced number ofparts required for construction, an easy control of the noise terminalvoltage, etc. With such advantages, a highly reliable switchingapparatus can be obtained, which is particularly suitable as theswitching regulator for use in computers requiring a low voltage and alarge load current.

What is claimed is:
 1. A magnetic core for use in a saturable reactor,made of an Fe-based soft-magnetic alloy comprising as essential alloyingelements Fe, Cu and M, wherein M is at least one element selected fromthe group consisting of Nb, W, Ta, Zr, Hf, Ti and Mo, and having analloy structure at least 50% in area ratio of which being finecrystalline particles having an average particle size of 100 nm or less,said magnetic core having, when measured at a core temperature of 25° C.using a 50 kHz monopolar rectangular voltage with an on-duty ratio of0.5, control magnetizatizing properties of: 0.12 T or less of a residualoperating magnetic flux density ΔBb; 2.0 T or more of a total controloperating magnetic flux density ΔBr; and 0.10-0.20 T/(A/m) of a totalcontrol gain Gr calculated by the equation: Gr=0.8×(ΔBr−ΔBb)/Hr whereinHr is a total control magnetizing force defined as a control magnetizingforce corresponding to 0.8×(ΔBr−ΔBb)+ΔBb.
 2. A multi-output switchingregulator having a magnetic amplifier comprising a saturable reactor,wherein said saturable reactor has the magnetic core as defined in claim1 .
 3. The multi-output switching regulator according to claim 2 ,wherein said multi-output switching regulator comprises: a primarycircuit comprising an input power source, a switching element and aprimary winding of a main transformer; and a secondary circuitcomprising a main output circuit for controlling a main output by apulse-width controlling operation of said switching element and asecondary output circuit comprising said magnetic amplifier forcontrolling a secondary output, said main output circuit and saidsecondary output circuit being respectively connected to the samesecondary winding of said main transformer.
 4. The multi-outputswitching regulator according to claim 3 , wherein an output voltage ofsaid main output is +5V and an output voltage of said secondary outputis +3.3V.
 5. The multi-output switching regulator according to claim 2 ,wherein a switching frequency is 30-150 kHz.
 6. A computer equipped withthe multi-output switching regulator according to claim 2 .